Carboxylic acids, such as acetic acid, may be commercially produced by alcohol carbonylation. Unfortunately, carbonylation processes create unwanted byproducts. Significant energy has been devoted to the removal of such byproducts, including a variety of processes and techniques. However, such processes and techniques can be complicated and costly.
Permanganate time (PT) is a quality test used industry wide for glacial acetic acid (GAA). The PT test can be utilized to determine the amount of oxidizable impurities present in a GAA product comprising low levels (e.g., less than or equal to 2000 ppm) of oxidizable impurities. Oxidizable impurities or ‘permanganate reducing compounds’ (PRCs), include, without limitation, saturated and unsaturated carbonyl compounds including acetaldehyde, acetone, crotonaldehyde, 2-ethyl crotonaldehyde and associated aldol condensation products. In contrast to GAA product which contains ppm levels of oxidizable impurities, intermediate process streams such as decanter light or heavy phases, may contain weight percent levels of these impurities. Some methods attempt removal of permanganate reducing compounds from decanter light or heavy phases via techniques such as oxidation or multiple distillation and/or aqueous extraction. Others describe removal of such compounds via pressure distillation or the addition of extra distillation columns. Other methods involve utilizing permanganate itself as a reducing agent in the process where aqueous or silica-supported KMnO4 added to the bottom of a distillation column is employed to remove oxidizable impurities such as acetaldehyde and crotonaldehyde. In addition to removal methods, various control methods have been proposed where the purpose is to limit the formation of acetaldehyde in the carbonylation reactor. Some such methods indicate a 25% improvement in permanganate time of a so-produced GAA product.
Conventional systems and methods for the removal of oxidizable impurities/PRCs from carboxylic acids can be costly and/or time consuming. Accordingly, a need exists for improved systems and methods for improving the permanganate time (oxidizable impurity content) of GAA without the need for conventionally employed removal methods and associated drawbacks. Disclosed herein are embodiments directed to providing such systems and methods.